Sepsis is the leading cause of death in noncoronary intensive care units in the US. A pathognomonic feature of sepsis is severe tissue injury secondary to a profound release of host cell cytokines. Activation of tumor necrosis factor receptor associated factor (TRAF) proteins is crucial to septic inflammation as these proteins link cell surface signals to cytokine release. The mechanistic platform of this proposal resides on our discovery of a unique molecular model of innate immunity for cytokine release whereby a relatively new protein, Fbxo3, potently stimulates cytokine secretion from human inflammatory cells by destabilizing a sentinel TRAF inhibitor, Fbxl2 (Nature Immunology 14:470-9, 2013). Our pilot data indicate that Fbxo3 and TRAF proteins in circulation positively correlate with cytokine responses in septic subjects. We also identified a hypofunctional Fbxo3 human polymorphism. By targeting the prokaryotic-like Fbxo3 ApaG molecular signature, we developed a unique genus of small molecule inhibitors that lessen severity of cytokine-driven inflammation in murine models. Hence, in this application we will elucidate how Fbxo3 degrades Fbxl2 (Aim 1), test a novel chemical entity acting as a Fbxo3 ApaG inhibitor in septic models (Aim 2), and biologically characterize a Fbxo3->TRAF pathway and naturally occurring polymorphism in a prospective cohort study in subjects with sepsis (Aim 3). These studies will provide a new pathway of innate immunity that may identify subjects with altered immune responses during critical illness or provide a basis for therapeutic intervention targeting TRAF protein abundance.